Non-volatile memory devices such as flash memory devices are used to store data or information. Many computers and electronic devices, for example, digital audio players, digital cameras, digital recorders, and cellular phones, have flash memory devices. Flash memory devices may also be used as portable storage devices such as portable Universal Serial Bus (USB) flash drives or “thumb” drives. Flash memory devices may not need power to maintain the information stored in the device.
A flash memory device stores information in numerous memory cells, which are usually formed in a semiconductor chip. Each of the memory cells often has a metal-oxide semiconductor (MOS) transistor with two different transistor gates: a control gate and a so-called “floating” gate. The control gate may be used to turn the transistor on and off to control access to the memory cell. The floating gate may be the place where one or more bits of information may be stored in each memory cell.
In a memory array, nearby cells may interfere with each other, specifically during programming phases. Programming a cell entails bringing that particular cell up to a specified voltage, Vt. Unfortunately, this process causes interference based on the changing voltage and capacitive coupling between nearby cells. This interference between floating gate transistors is referred to as Fg-Fg interference.
As technology advances and the size of devices get smaller and smaller, the scaling of memory cells decreases. This scaling moves the memory cells closer, and subjects them to increased interference as capacitive coupling becomes stronger.
Fg-Fg interference is a problem present in Single-Layer Cell (SLC) memory but is a bigger problem in Multi-Layer Cell (MLC) memory. Because there are more distributions in MLC memory, the changing voltage Vt can be even higher.